Generally, in a process in which a network device communicates with a terminal device in a communications system, a channel status affects quality of communication between the network device and the terminal device. However, data transmitted in different transmission locations in transmission resources undergoes different channel statuses. To ensure the quality of communication with the terminal device, the network device generally sends, to the terminal device in a downlink timeslot in each resource block (resource block, RB for short) that can be scheduled, a pilot used for channel measurement, so as to obtain precoding information. Specifically, the terminal device determines, according to the received pilot, a channel status undergone by a pilot in each RB. Subsequently, the terminal device traverses all precoding vectors in a configured precoding codebook according to a channel status undergone by a pilot in each RB, determines a precoding vector appropriate to each RB, and feeds back an index of a precoding vector appropriate to each RB to the network device, so that the network device uses an appropriate precoding vector when subsequently sending data information to the terminal device in each RB, so as to ensure the quality of communication with the terminal device.
As mobile communications continuously develops, a next generation cellular communications system is urgently required to improve a system throughput. MIMO (Multiple-Input Multiple-Output, multiple-input multiple-output) is a commonly used technology. That is, a large quantity of antennas are deployed on a network device side to improve the system throughput. Correspondingly, as the quantity of the antennas on the network device side increases, a quantity of pilots sent by the network device in each RB also continuously increases. Therefore, a pilot signal has relatively high overheads in one channel measurement process, and communication efficiency is reduced.